1. Field of the Invention
The present general inventive concept relates to a hard disk drive (HDD), and more particularly, to a retracting method of compensating for a time for parking or unloading of a head with an additional floating force obtained by additional driving of a spindle motor for a predetermined period after a retract operation is started, a hard disk drive (HDD) adopting the method, and a recording medium having a program to perform the method.
2. Description of the Related Art
A hard disk drive (HDD) is a recording device used to store information. In general, information is recorded on concentric tracks on a surface of at least one magnetic recording disk. A disk is mounted on a spindle motor to be rotated, and information is accessed by a head mounted on an actuator arm rotated by a voice coil motor (VCM). The VCM is excited by current to rotate an actuator and move a head.
The head senses a magnetic change generated from the surface of the disk to read information recorded thereon. In order to record data on the track, current is supplied to the head. The current generates a magnetic field, and the magnetic field magnetizes the disk surface.
In the HDD, a so-called retract operation of retracting the head to a parking zone or a ramp is performed when an idle state is continued more than a predetermined time, when an external shock is detected, when a free-fall is detected, when a drive of the HDD is terminated, and when a driving power of the HDD is suddenly blocked, in other words, when saving of power consumption is required or when the head and the disk need to be protected from an impact.
In the retract operation, a spindle motor driving power is blocked. Thus, the spindle motor becomes to rotate freely with a rotational inertia of the disk. In addition, the head is moved to the parking zone or unloaded onto the ramp by applying a back electromotive force generated by free rotation of the spindle motor to a VCM driver.
FIG. 1 illustrates a hard disk drive 100 adopting a parking method. Referring to FIG. 1, the hard disk drive 100 includes at least one disk 12 rotated by a spindle motor 14. The hard disk drive 100 further includes a head 16 that is located adjacent to the surface of the disk 12.
The head 16 can read or record information from or on the disk 12 that rotates, by sensing a magnetic field formed on the surface of the disk 12 or magnetizing the surface of the disk 12, respectively. Although a single head 16 is shown in FIG. 1, it should be understood that the head 16 includes a recording head for magnetizing the disk 12 and a separate reading head for sensing the magnetic field of the disk 12.
The head 16 is integrated with a slider (not shown) into a single unit, wherein the slider is configured to generate an air bearing between the head 16 and the surface of the disk 12. The slider is attached to a suspension 20, and the suspension 20 is combined with a head stack assembly (HSA) 22. The HAS 22 is attached to an actuator arm 24 having a voice coil 26. The voice coil 26 is located adjacent to a magnetic assembly 28 that defines a voice coil motor (VCM). A VCM driving current supplied to the voice coil 26 through a cable line 38 generates a torque to rotate the actuator arm 24 around a bearing assembly 32. Rotation of the actuator arm 24 may cause the head 16 to move across the surface of the disk 12. The cable line 38 is connected between a main controller (not shown) and the head 16 and the magnet assembly 28 to transmit data between the head 16 and the main controller and to transmit signals to control the magnet assembly 28 to move the head 16 with respect to the disk 12.
Information is stored in tracks of the disk 12. In general, the disk 12 includes a data zone 34, on which data is recorded, and a parking zone 36, on which the head 16 is parked.
In a retract operation of the hard disk drive 100 illustrated in FIG. 1, the head 16 is moved to an inner circumference of the disk 12, i.e., to the parking zone 36 illustrated by a dotted line of FIG. 1, by a back electromotive force generated in the spindle motor 14. The back electromotive force is detected, and a signal corresponding to the detected back electro-motive force is transmitted to the voice coil 26 of the VCM of the magnetic assembly 28, for example, through the cable line 38.
FIG. 2 illustrates a structure of a latch mechanism A of the hard disk drive 100 illustrated in FIG. 1. When the head 16 is moved to the parking zone 36, the latch mechanism A latches the actuator 22 so that the actuator 22 does not move. The latch mechanism A includes an iron-piece 40, which extends from an end of the actuator arm 24, and a permanent magnet 42 to attract the iron-piece 40 with its magnetic force.
FIG. 3 illustrates a hard disk drive adopting a ramp method. Since a ramp structure of a ramp 6 of FIG. 3 can be used in the hard disk drive of FIG. 1, like reference numerals denote like elements, and a detailed description thereof will be omitted.
In the retract operation, the HDD illustrated in FIG. 3 moves the head 16 to be placed on the ramp 6 installed in a side of the outer circumference of the disk 12 by the back electro-motive force generated in the spindle motor 14.
FIG. 4 is a cross-sectional view illustrating the ramp 6 of FIG. 3. As shown in FIG. 4, in the retract operation, the head 16 rises along an inclined surface 6d and is seated on a seating surface 6a. A protrusion 20a is installed under the slider (suspension) 20 to contact the ramp 6.
Recently, in accordance with increase of use of mobile devices adopting the hard disk drive, a size of the hard disk drive is gradually reduced. This means that the size and a rotational inertia of the disk, on which information is recorded, are reduced and the back electro-motive force generated in the spindle motor is reduced as well.
Therefore, in such a hard disk drive having a smaller size, it is difficult to obtain enough back electro-motive force from a spindle motor to move a head to the parking zone or raise the head onto the ramp.
In the retract operation, the head should be moved near to the parking zone while the disk is freely rotated by the rotational inertia or the head should be moved to the ramp while the back electro-motive force generated in the spindle motor is sufficient to raise the head along the incline of the ramp.
If the back electro-motive force generated in the spindle motor is not sufficient to move the head near to the parking zone or to the ramp, or to climb the head along the inclined surface of the ramp to be seated on a rest area of the ramp, the head becomes to land on the data area of the disk. Consequently, the head and the disk may be damaged.
FIGS. 5A-5D are graphs schematically illustrating a conventional retracting method in a case where a driving power of the hard disk drive 100 of FIG. 1 is suddenly blocked. FIG. 5A shows the driving power of the hard disk drive 100, FIG. 5B shows a power of reset signal (POR) generated when the driving power of the hard disk drive 100 falls less than a predetermined threshold value th1, FIG. 5C shows a desirable rotating speed of the spindle motor 14, and FIG. 5D shows an undesirable rotating speed of the spindle motor 14.
Referring to FIGS. 5A and 5B, the power reset signal POR is generated when the driving power of the hard disk drive 100 falls less than the predetermined threshold value th1, and the retract operation is started from a point of time t0. The threshold value th1 is about 15% lower than a regular driving power of the hard disk drive 100, for example, a driving power to drive the spindle motor 14 to rotate the disk to read or write data from or on the disk 12.
If the power reset signal POR is generated, a spindle motor driving power applied to the spindle motor driver driving the spindle motor 14 is blocked immediately. Accordingly, the spindle motor 14 freely rotates according to a rotational inertia of the disk 12 to generate the back electro-motive force. The back electro-motive force can control the voice coil to move the head to the ramp 6 or the parking zone 36.
Referring to FIG. 5C, the rotation speed of the spindle motor 14 decreases along the lapse of the time because of friction between the air and the disk 12 and a rotational friction of the spindle motor 14. If the rotational inertia of the disk 12 is sufficient, at a point of time t1, the head 16 can be moved near to the parking zone 36 or to the ramp 6. After a point of time t1, the head 16 is parked on the parking zone 36 or is raised onto the ramp 6.
In the hard disk drive 100 adopting the parking method, if the head 16 is completely moved to the parking zone 36, the actuator (actuator arm 24) is fixed by the operation of the latch mechanism A. Further, as the rotation speed of the spindle motor 14 decreases, a head-floating force is reduced and thus the head 16 becomes to land on the parking zone 36.
In the meantime, in the hard disk drive 100 adopting the ramp method, the head 16 rises along the inclined surface of the ramp 6 and is seated on the seating surface by the back electro-motive force generated in the spindle motor 14.
However, when the rotational inertia of the disk 12 is not large enough, a normal retract operation cannot be performed. When the retract condition is detected, supply of the spindle motor driving power to the spindle motor is terminated. Since the spindle motor is driven by the rotational inertia of the disk, the rotation speed of the spindle motor 14 decreases to generate a small amount of the back electro-motive force which is not enough to control the voice coil to move the head to the retract area, such as the parking zone 36 or the ramp 6.
As shown in graph 52 of FIG. 5D, if the back electromotive force generated in the spindle motor 14 is not sufficient to move the head 16 to the parking zone 36 or to the ramp 6, the head 16 becomes to land on the data area 34 of the disk 12. In the meantime, as shown in graph 54 of FIG. 5D, in the hard disk drive 100 adopting the ramp method, if the back electro-motive force generated in the spindle motor 14 at the point of time t1 is not sufficient as much as the head can be raised onto the ramp 6, that is, if the rotating speed of the spindle motor 14 is less than a threshold value th2, the head 16 cannot be raised onto the ramp 6 and becomes to land on the data area 34 of the disk 12.
In the meantime, in order to compensate for an insufficient back electromotive force generated in the spindle motor 14, it can be considered to rapidly move the head 16. However, in this case, due to an inertia caused by a fast move, the head 16 collides to a crash stop (not shown) or shock when the head 16 is stop becomes very large even though the head 16 is raised onto the ramp 6. Thus, the head 16 may be damaged.